The girls. Tatas. The twins. Whatever you choose to call them, you have to admit that breasts are pretty amazing. They're both beautiful and functional (breastfeeding, anyone?), but oftentimes we don't give them much thought unless they're tender right before our period arrives or because we're on the hunt for the right bra.

But how much do we actually know about our mammaries? Here are eight interesting facts worth knowing about your pair.

1. Breasts don't come in matching sets.

"Nobody has a 'perfect' pair of breasts," Nolan S. Karp, M.D., associate professor in the Hansjorg Wyss Department of Plastic Surgery at NYU Langone Medical Center, tells SELF. "No one is ever perfectly symmetrical." Although Karp has noticed in his practice that the left breast tends to be bigger than the right, one study found that the right breast is slightly bigger than the left.

2. Breasts have no muscle.

They're made up of tissue, fat, and glands. Breasts sit on top of the pectoral muscles, but breasts themselves don't have any muscle in them. So you can do push-ups your arms give out, but it's not going to make your set any perkier (sorry).

3. They don’t just bounce when you run—they dance.

When you jog or run, your breasts can bounce more than eight inches and move in all different directions—not just up and down, but also side-to-side, in and out, and in figure eights, according to a British study. (Yes, they actually did a study to test this.) With an estimated 50 percent of women dealing with breast pain while exercising, the study authors hope their research will lead to creating more supportive bras for women.

4. And pain from that movement has nothing to do with how big they are.

The same study found that breast pain during exercise was just as bad for women with A-cups as FFs. The research included women with cup sizes up to JJ.

5. They are pretty much eye magnets—for everyone.

Turns out, you may need to tell both men and women that your eyes are up here. A 2013 study in the journal Sex Roles had participants look at a series of photos while tracking their eye gaze and found that both sexes focused more on cleavage and waistlines than faces, especially if the women in the photos had an hourglass shape.

6. Nipples are the clitorises of the upper body.

A whopping 82 percent of women say that having their nipples and breasts stimulated gets them aroused, according to study in the Journal of Sexual Medicine. "The breast's nipples and areola are rich in blood vessels and nerves, so they're really erogenous zones," says Alyssa Dweck, M.D., assistant clinical professor of obstetrics at Mount Sinai School of Medicine and co-author of V is For Vagina. A Rutgers University study may explain why: The researchers found that sensation from the nipples light up the same areas of the brain as sensations from the clitoris and vagina.

7. You can have an extra nipple, and they’re twice as common in women.

Accessory nipples—which make them sound more like a fun pair of earrings—are more common than you think. Up to six percent of women have them (and up to three percent of men). Extra nipples tend to run down the milk line, meaning below and in line with your original nipple like other mammals.

8. People will shell out big bucks for breast milk.

It's basically liquid gold—and we're not just talking for babies. Breast milk has become a lucrative market thanks to adults, from CrossFit fanatics to chronic disease sufferers, who see it as an immune-boosting, protein-rich superfood, according to a 2015 study. But keep in mind that, while breast milk is nutritionally rich for growing babies, there's little evidence that adults consuming raw breast milk are gaining any benefits beyond a placebo effect, according to the study's researchers. What's more, if the pumped breast milk isn't stored properly, it can carry bacteria. HIV is also a concern, as it can be transmitted through breast milk. Breast milk banks screen donations for HIV, hepatitis and other diseases such as syphilis. The Internet, however, does not, so be very wary about buying breast milk on the booby black market.